An experimental hepatitis C drug combination from Gilead Sciences Inc. wiped out all strains of the virus in a large clinical trial, giving the company an advantage against AbbVie Inc. in the race to treat as many patients as possible.

In a trial of 624 patients with any of six strains, or genotypes, of hepatitis C, Gilead’s experimental combination of velpatasvir and sofosbuvir was effective at clearing the virus 99 percent of the time after 12 weeks of therapy. Three related trials also showed the drug was successful in treating multiple strains, the Foster City biotech company said this week.